from US address to US address, i would say 3-5 business days is safe.
but international, maybe up to 2 weeks lol. and if you didnt leave an email in your letter he cant email you the key. so you have to wait even longer for a letter to return.
not to mention if you sent a check, he wont even think about mailing you anything till it clears in the bank. another 5-7 days out of town check.